Table 1. Comparison of amino acid frequencies in all annotated proteins among free-living (Free) and pathogenic (Path) microbes.

Amino Acid	GFM	FREE (mean frequency)	PATH (mean frequency)	p-value
A	89	0.0948	0.0860	2.060e-05
C	121	0.0094	0.0097	NS
D	133	0.0539	0.0531	NS
E	147	0.0635	0.0614	2.833e-03
F	165	0.0396	0.0434	1.035e-11
G	75	0.0756	0.0686	2.263e-16
H	155	0.0199	0.0208	2.624e-04
I	131	0.0647	0.0702	2.213e-04
K	146	0.0515	0.0604	7.478e-07
L	131	0.1021	0.1023	NS
M	149	0.0237	0.0240	NS
N	132	0.0373	0.0452	1.511e-12
P	115	0.0453	0.0399	2.675e-14
Q	147	0.0341	0.0389	1.220e-13
R	174	0.0576	0.0490	1.103e-12
S	105	0.0589	0.0621	1.061e-08
T	119	0.0526	0.0529	NS
V	117	0.0725	0.0676	1.375e-12
W	181	0.0120	0.0110	1.883e-05
Y	204	0.0301	0.0324	2.772e-05

A Welsh’s two-sample t-test was used to compare the mean frequencies and test for the likelihood that the difference among Free and Path observations was not zero. This statistic essentially establishes a 95% confidence interval around the difference of means and assigns significance based on how far the observed arithmetic difference is from 0.